So I tried to like military press the pedal cages up and there's no play or flex at all in those anymore. They move with the car's suspension now.
I put the shifter and e-brake back in today, locked out the rear wheels and cranked the axle nuts to about 250 pounds. Looks-wise I think the interior's as good as it's going to get, in terms of fealty to the original cars.
This is 550-0018's interior as photographed from behind the driver's head.
And here's my car from a similar vantage point:
Steering wheel's a little smaller. Shifter is a little shorter. Shift housing is a little bigger. But it's in the ball park. I'm OK with it...